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## Creator

[Jedeok KIM](https://orcid.org/0000-0003-4301-1044), Kazuya Yamasaki, Hitoshi Ishimoto, Yusuke Takata

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[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

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[Ultrathin Electrolyte Membranes with PFSA-Vinylon Intermediate Layers for PEM Fuel Cells](https://mdr.nims.go.jp/datasets/bde41483-e05a-4fa2-bb64-d955ad8b5c0f)

## Fulltext

Ultrathin Electrolyte Membranes with PFSA-Vinylon Intermediate Layers for PEM Fuel CellspolymersCommunicationUltrathin Electrolyte Membranes with PFSA-VinylonIntermediate Layers for PEM Fuel CellsJedeok KIM 1,2,* , Kazuya Yamasaki 3, Hitoshi Ishimoto 3 and Yusuke Takata 31 Hydrogen Production Materials Group, Center for Green Research on Energy and Environmental Materials,National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan2 Functional Clay Materials Group, Research Center for Functional Materials,National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan3 Engineering Division, Industrial Solutions Company, Panasonic Corporation, 1006 Kadoma, Kadoma City,Osaka 571-8506, Japan; yamasaki.kazuya001@jp.panasonic.com (K.Y.);ishimoto.hitoshi@jp.panasonic.com (H.I.); takata.y@jp.panasonic.com (Y.T.)* Correspondence: kim.jedeok@nims.go.jp; Tel.: +81-29-860-4764; Fax: +81-29-860-4984Received: 18 July 2020; Accepted: 27 July 2020; Published: 3 August 2020�����������������Abstract: We prepared ultrathin PFSA/PFSA-vinylon/PFSA laminated electrolyte membranes(thickness = 10 µm) for fuel cells without using a reinforcing material. Nafion and Aquivion solutionswere used as PFSA polymers. Vinylon was synthesized by formalizing polyvinyl alcohol. From thecurrent-voltage measurements using ultrathin PFSA/PFSA-vinylon/PFSA membranes; the cell resistancesare significantly lower than that using a 50 µm Nafion membrane. A high current density was obtainedunder both low- and high-humidity conditions. Ultrathin PFSA/PFSA-vinylon/PFSA laminated membraneswill help to further improve the performance of PEMFCs.Keywords: PFSA ionomers; PFSA-vinylon; lamination; THIN membrane; fuel cells1. IntroductionFuel cells, water electrolysis devices, secondary batteries, redox flow batteries (RFBs), solarcells, etc., are attracting attention as important energy devices for realizing a CO2-free society.Research to improve the performance of these devices and systems is actively being conducted.The performance and durability of fuel cells have been improving while their system costs havereduced, and they are being used in mobile and stationary applications. However, in order to becommercialized, the constituent materials must be made cheaper, and the performance and durabilitymust be higher. One way to achieve low cost and high performance is to decrease the thicknessesof the polymer electrolyte membranes. Proton exchange fuel cells utilize a polymer electrolytecomposed of perfluorosulfonic acid (PFSA) type ionomers, such as DuPont’s Nafion and, more recently,3M’s and Solvay’s ionomers [1]. The thickness of the electrolyte membranes has been reduced from178–25 µm for a Nafion membrane to 20–5 µm for a GORE-SELECT® membrane [2,3]. Thinning thepolymer electrolyte membrane can improve the performance by reducing the ohmic voltage drop ofthe fuel cell and can reduce the cost. However, extremely thin polymer electrolyte membranes aredifficult to handle when assembling a fuel cell, and their durabilities are lower. On the other hand, theGORE-SELECT® membrane, which uses expanded polytetrafluoroethylene (ePTFE) as a reinforcingmaterial, is a thin membrane that can be handled reliably and has a high durability, but it is costly [3–5].Therefore, a highly durable thin membrane without reinforcing materials that is easy to handle wouldbe useful as an electrolyte membrane. There has been a report of a Nafion/sulfonated polyimide(SPI)/Nafion composite membrane without a reinforcing membrane with a thickness of 15 µm [6].However, it is a layered membrane prepared by dipping a hydrocarbon-based SPI membrane, which isPolymers 2020, 12, 1730; doi:10.3390/polym12081730 www.mdpi.com/journal/polymershttp://www.mdpi.com/journal/polymershttp://www.mdpi.comhttps://orcid.org/0000-0003-4301-1044http://www.mdpi.com/2073-4360/12/8/1730?type=check_update&version=1http://dx.doi.org/10.3390/polym12081730http://www.mdpi.com/journal/polymersPolymers 2020, 12, 1730 2 of 6an engineering plastic with a thickness of 11 µm, into a Nafion solution. There are no reports of fuelcell evaluation using an ultrathin PFSA membrane of 10 µm or less without a reinforcing material.In this communication, we prepared an ultrathin laminated membrane of PFSA/PFSA-vinylon/PFSAthat could be handled even when the thickness was under 10 µm by inserting a PFSA-vinylon compositelayer between PFSA electrolyte membranes. Vinylon has high hydration stability and scale stability, so it issuitable as an additive material for thin membrane formation. In addition, it was determined to have a highcurrent density from fuel cell evaluations.2. ExperimentalNafion (5%, DE520 CS type, equivalent weight (EW) = 1100) and Aquivion solutions (6%, D83-06A,equivalent weight (EW) = 830) were purchased from Fujifilm Wako Pure Chemical Corporation (Osaka,Japan) and Solvay (Tokyo, Japan), respectively. Polyvinyl acetate (PVAc, (C4H6O2)n, Mw = 86.09 g/mol,Mw = 100,000) was purchased from Sigma-Aldrich Co., Ltd. (St. Louis, MO, USA). Sodium hydroxide(NaOH), methanol (CH3OH), formaldehyde (HCHO, 37%), sodium sulfate (Na2SO4), hydrogenperoxide (H2O2), sulfuric acid (H2SO4), and sodium chloride (NaCl) were purchased from NacalaiTesque (Kyoto, Japan). A Nafion212 (NR212) membrane was purchased from DuPont (USA). DI waterwas obtained using a Purelab® Option-R ELGA Labwater (25 ◦C, 15 Mohm cm).The synthesis of polyvinyl alcohol (PVA) has been described in a previous paper [7]. The PFSA-PVAmixed solution was prepared using the following method. To obtain a uniform mixture, the amount ofPVA added for Nafion was 5 wt % PVA, and 1 wt % PVA was added for Aquivion.The PFSA/PFSA-PVA/PFSA membrane was prepared as follows. A polyimide sheet (27 cm× 30 cm)was placed on a coater (KP-3000VH, KIPAE CO. Ltd., Suwon, Korea) and coated with an applicator(Tester Sangyo CO. Ltd., Saitama, Japan; 15 cm, gap = 0.1 mm) at room temperature. Before producingthe laminated membrane, the membrane thickness was controlled by using a single membrane, and thenthe laminated membrane was prepared. First, 2 µm PFSA layer membranes were coated and thendried. Then, intermediate layers of 6 µm PFSA-PVA layer membranes were coated and then dried,and finally, a 2 µm PFSA layer membrane was coated and dried. Then the membranes were heated at60 ◦C for 3 h, followed by 180 ◦C for 3 h, to obtain 10 µm PFSA/PFSA-PVA/PFSA laminated membranes.To form vinylon, the PFSA/PFSA-PVA/PFSA membranes were added to a formalization solutionwith a mass ratio of H2O:H2SO4:Na2SO4:CH2O of 1.00:0.21:0.20:0.06 at 60 ◦C for 2 h and were thenwashed with water to afford PFSA/PFSA-vinylon/PFSA membranes. They were activated with boilingwater (2 h), 1M H2SO4 (80 ◦C, 2 h), and boiling water (2 h) and dried at room temperature.The ion exchange capacity (IEC), water-uptake (W.U.), and proton conductivity were measuredby using the methods reported in our previous paper [8]. The chemical structure of the sample wasdetermined using attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopyon a Thermo Scientific Nicolet 6700 spectrometer. The PFSA/PFSA-PVA/PFSA membranes used forfuel cell measurements had a thickness of 10 µm, and the Nafion212 membrane used for comparisonhad a thickness of 50 µm. A catalyst ink was prepared by mixing 50 wt % Pt/C (TEC10E50E,Tanaka Kikinzoku Kogyo K.K.) and 20 wt % Nafion ionomer (DE2020, Fujifilm Wako Pure ChemicalCorporation). The mass ratio of the binder and carbon balance (ionomer/carbon) was adjusted to 1.0.The catalyst ink (0.3 mg-Pt cm−2) was formed on the gas diffusion layer (GDL) (SGL Group Co. Ltd.,Tokyo, Japan) and hot-pressed at 140 ◦C and 1 MPa for 5 min to fabricate a membrane electrodeassembly (MEA). The effective electrode area of the single cell was 4 cm2. I–V characteristics weremeasured at 80 ◦C and atmospheric pressure under 100% and 35% RH using hydrogen for the anodeand air or oxygen for the cathode. The flow rates of the gases were controlled using a mass flowcontroller (MFC). The amounts of reaction gases were 75% for hydrogen (H2) and 55% for oxygen (O2).3. Results and DiscussionFigure 1 shows a photograph and a schematic diagram of an ultrathin Nafion/Nafion-vinylon/Nafionmembrane, and the chemical structure of the intermediate Nafion-vinylon layer. Although it is difficult toPolymers 2020, 12, 1730 3 of 6handle the ultrathin PFSA membrane alone (10 µm), ultrathin PFSA/PFSA-vinylon/PFSA membranes withthicknesses of 10 µm or less could be handled. It is thought that the mechanical properties are improved byadding a PFSA-vinylon layer. From a cross-sectional observation of the PFSA/PFSA-vinylon/PFSA membraneby using scanning electron microscopy (SEM), the laminated membranes could not be distinguished. Since thelayers were composed of the same components, there may have been no interface. However, a more detailedstructural analysis is required.Polymers 2020, 12, x FOR PEER REVIEW 3 of 6  Figure 1 shows a photograph and a schematic diagram of an ultrathin Nafion/Nafion-vinylon/Nafion membrane, and the chemical structure of the intermediate Nafion-vinylon layer. Although it is difficult to handle the ultrathin PFSA membrane alone (10 μm), ultrathin PFSA/PFSA-vinylon/PFSA membranes with thicknesses of 10 μm or less could be handled. It is thought that the mechanical properties are improved by adding a PFSA-vinylon layer. From a cross-sectional observation of the PFSA/PFSA-vinylon/PFSA membrane by using scanning electron microscopy (SEM), the laminated membranes could not be distinguished. Since the layers were composed of the same components, there may have been no interface. However, a more detailed structural analysis is required.  Figure 1. Ultrathin Nafion/Nafion-vinylone/Nafion membrane, schematic diagram, and Nafion-vinylon chemical structure. The existence of vinylon in the ultrathin PFSA/PFSA-vinylon/PFSA membrane was investigated by using FTIR. Figure 2 shows FTIR spectra for Aquivion only and Aquivion/Aquivion-vinylon/Aquivion membranes. In the spectrum of the Aquivion/Aquivion-vinylon/Aquivion membrane, peaks for vinylon were observed at 2918 cm−1 (vas, CH2) and 2842 cm−1 (vs, CH2) in addition to a peak for Aquivion. From these results, the presence of vinylon in the ultrathin membrane was confirmed.  Figure 2. FTIR spectra for (a) Aquivion and (b) an Aquivion/Aquivion-vinylon/Aquivion membrane. The conductivities of the laminated ultrathin membranes were measured in relation to the relative humidity at 40 and 80 °C. Figure 3 shows the conductivity characteristics of the Nafion/Nafion-vinylon/Nafion and Aquivion/Aquivion-vinylon/Aquivion membranes. The Figure 1. Ultrathin Nafion/Nafion-vinylone/Nafion membrane, schematic diagram, and Nafion-vinylonchemical structure.The existence of vinylon in the ultrathin PFSA/PFSA-vinylon/PFSA membrane was investigated byusing FTIR. Figure 2 shows FTIR spectra for Aquivion only and Aquivion/Aquivion-vinylon/Aquivionmembranes. In the spectrum of the Aquivion/Aquivion-vinylon/Aquivion membrane, peaks forvinylon were observed at 2918 cm−1 (vas, CH2) and 2842 cm−1 (vs, CH2) in addition to a peak forAquivion. From these results, the presence of vinylon in the ultrathin membrane was confirmed.Polymers 2020, 12, x FOR PEER REVIEW 3 of 6  Figure 1 shows a photograph and a schematic diagram of an ultrathin Nafion/Nafion-vinylon/Nafion membrane, and the chemical structure of the intermediate Nafion-vinylon layer. Although it is difficult to handle the ultrathin PFSA membrane alone (10 μm), ultrathin PFSA/PFSA-vinylon/PFSA membranes with thicknesses of 10 μm or less could be handled. It is thought that the mechanical properties are improved by adding a PFSA-vinylon layer. From a cross-sectional observation of the PFSA/PFSA-vinylon/PFSA membrane by using scanning electron microscopy (SEM), the laminated membranes could not be distinguished. Since the layers were composed of the same components, there may have been no interface. However, a more detailed structural analysis is required.  Figure 1. Ultrathin Nafion/Nafion-vinylone/Nafion membrane, schematic diagram, and Nafion-vinylon chemical structure. The existence of vinylon in the ultrathin PFSA/PFSA-vinylon/PFSA membrane was investigated by using FTIR. Figure 2 shows FTIR spectra for Aquivion only and Aquivion/Aquivion-vinylon/Aquivion membranes. In the spectrum of the Aquivion/Aquivion-vinylon/Aquivion membrane, peaks for vinylon were observed at 2918 cm−1 (vas, CH2) and 2842 cm−1 (vs, CH2) in addition to a peak for Aquivion. From these results, the presence of vinylon in the ultrathin membrane was confirmed.  Figure 2. FTIR spectra for (a) Aquivion and (b) an Aquivion/Aquivion-vinylon/Aquivion membrane. The conductivities of the laminated ultrathin membranes were measured in relation to the relative humidity at 40 and 80 °C. Figure 3 shows the conductivity characteristics of the Nafion/Nafion-vinylon/Nafion and Aquivion/Aquivion-vinylon/Aquivion membranes. The Figure 2. FTIR spectra for (a) Aquivion and (b) an Aquivion/Aquivion-vinylon/Aquivion membrane.The conductivities of the laminated ultrathin membranes were measured in relation to the relativehumidity at 40 and 80 ◦C. Figure 3 shows the conductivity characteristics of the Nafion/Nafion-vinylon/Nafionand Aquivion/Aquivion-vinylon/Aquivion membranes. The conductivity of the ultrathin laminatedmembranes increased with increases in the temperature and the humidity. The conductivityof Aquivion/Aquivion-vinylon/Aquivion was higher than that of Nafion/Nafion-vinylon/Nafion.The IEC of Nafion/Nafion-vinylon/Nafion was 1.12 meq/g, and the W.U. was 50%. The IEC ofPolymers 2020, 12, 1730 4 of 6Aquivion/Aquivion-vinylon/Aquivion was 1.46 meq/g, and the W.U. was 86%. The higher conductivity ofthe Aquivion-based membrane in comparison to the Nafion-based membrane was due to the high IECand W.U. Moreover, the conductivity depended on the membrane thickness, meaning that the conductivitydecreased with a decrease in the thickness. A Nafion212 membrane with a thickness of 50 µm has beenreported to have a conductivity of about 0.1 S/cm at 80 ◦C under 90% RH [1,8,9].Polymers 2020, 12, x FOR PEER REVIEW 4 of 6  conductivity of the ultrathin laminated membranes increased with increases in the temperature and the humidity. The conductivity of Aquivion/Aquivion-vinylon/Aquivion was higher than that of Nafion/Nafion-vinylon/Nafion. The IEC of Nafion/Nafion-vinylon/Nafion was 1.12 meq/g, and the W.U. was 50%. The IEC of Aquivion/Aquivion-vinylon/Aquivion was 1.46 meq/g, and the W.U. was 86%. The higher conductivity of the Aquivion-based membrane in comparison to the Nafion-based membrane was due to the high IEC and W.U. Moreover, the conductivity depended on the membrane thickness, meaning that the conductivity decreased with a decrease in the thickness. A Nafion212 membrane with a thickness of 50 μm has been reported to have a conductivity of about 0.1 S/cm at 80 °C under 90% RH [1,8,9].  Figure 3. Proton conductivities of Nafion/Nafion-vinylon/Nafion (a) at 40 and (b) 80 °C and Aquivion/Aquivion-vinylon/Aquivion (c) at 40 and (d) 80 °C. Recast ultrathin membranes of about 10 μm prepared using Nafion and Aquivion solutions are difficult to handle, and they are easily broken. However, the laminated ultrathin membranes could be handled even with a thickness of 10 μm or less, and the fuel cell performance could be evaluated. Figure 4 shows the results of current-voltage (I–V) and current-resistance (I-R) measurements made using fuel cells with MEAs fabricated with 10 μm Nafion/Nafion-vinylon/Nafion and Aquivion/Aquivion-vinylon/Aquivion membranes. In addition, the characteristics of a Nafion212 membrane with a thickness of 50 μm are shown for comparison. The measurements were performed at a cell temperature of 80 °C under 100% RH and 35% RH conditions. The anode gas was hydrogen, and the cathode gas was air and oxygen. From Figure 4, the resistances of the fuel cells using the 10 μm laminated ultrathin membranes were significantly lower in comparison to the resistances of the fuel cell using the 50 μm Nafion212 membrane. This is because thinning an electrolyte membrane reduces the cell resistance of a fuel cell. Due to the low resistance, the I–V performances of the fuel cells using the laminated ultrathin membranes were significantly better than those using the Nafion212 membrane. In addition, the I–V performances of the fuel cells using the laminated ultrathin membranes and the Nafion212 membrane were more remarkable when oxygen was used than when air was used as the cathode gas. Furthermore, the Aquivion/Aquivion-vinylon/Aquivion membrane was stable with no increase in the resistance even at a high current density of 3 A/cm2. On the other hand, the open-circuit voltage of the fuel cells using the 10 μm laminated ultrathin membranes decreased. This indicates that the gas barrier properties of the laminated ultrathin membranes are lower than those of the Nafion212 membrane, and therefore, it is necessary to improve the gas barrier properties. Table 1 summarizes these characteristics. Figure 3. Proton conductivities of Nafion/Nafion-vinylon/Nafion (a) at 40 and (b) 80 ◦C and Aquivion/Aquivion-vinylon/Aquivion (c) at 40 and (d) 80 ◦C.Recast ultrathin membranes of about 10 µm prepared using Nafion and Aquivion solutionsare difficult to handle, and they are easily broken. However, the laminated ultrathin membranescould be handled even with a thickness of 10 µm or less, and the fuel cell performance couldbe evaluated. Figure 4 shows the results of current-voltage (I–V) and current-resistance (I-R)measurements made using fuel cells with MEAs fabricated with 10 µm Nafion/Nafion-vinylon/Nafionand Aquivion/Aquivion-vinylon/Aquivion membranes. In addition, the characteristics of a Nafion212membrane with a thickness of 50 µm are shown for comparison. The measurements were performedat a cell temperature of 80 ◦C under 100% RH and 35% RH conditions. The anode gas was hydrogen,and the cathode gas was air and oxygen.From Figure 4, the resistances of the fuel cells using the 10 µm laminated ultrathin membraneswere significantly lower in comparison to the resistances of the fuel cell using the 50 µm Nafion212membrane. This is because thinning an electrolyte membrane reduces the cell resistance of a fuelcell. Due to the low resistance, the I–V performances of the fuel cells using the laminated ultrathinmembranes were significantly better than those using the Nafion212 membrane. In addition, the I–Vperformances of the fuel cells using the laminated ultrathin membranes and the Nafion212 membranewere more remarkable when oxygen was used than when air was used as the cathode gas. Furthermore,the Aquivion/Aquivion-vinylon/Aquivion membrane was stable with no increase in the resistance evenat a high current density of 3 A/cm2. On the other hand, the open-circuit voltage of the fuel cells usingthe 10 µm laminated ultrathin membranes decreased. This indicates that the gas barrier properties ofthe laminated ultrathin membranes are lower than those of the Nafion212 membrane, and therefore,it is necessary to improve the gas barrier properties. Table 1 summarizes these characteristics.Polymers 2020, 12, 1730 5 of 6Polymers 2020, 12, x FOR PEER REVIEW 5 of 6   Figure 4. I–V characteristics of (i) Nafion212, (ii) Nafion/Nafion-vinylon/Nafion, and (iii) Aquivion/Aquivion-vinylon/Aquivion at 80 °C in (a) air and (b) O2 under 100% RH and in (c) air and (d) O2 under 35% RH. Table 1. I–V performance summary for the (i) Nafion212, (ii) Nafion/Nafion-vinylon/Nafion, and (iii) Aquivion/Aquivion-vinylon/Aquivion membranes.  Membranes 100% RH 35% RH Air O2 Air O2 Resistance (mohm) at 0.3 A/cm2 Rate (%) of Decreasing Resistance Resistance (mohm) at 2.5 A/cm2 Rate (%) of Decreasing Resistance Resistance (mohm) at 0.3 A/cm2 Rate (%) of Decreasing Resistance Resistance (mohm) at 2.5 A/cm2 (i) 15.6 100 20.8 100 60.8 100 _ (ii) 6.5 45 8.0 38 16.7 27 26.4 (iii) 6.5 45 7.7 37 25.1 41 20.3 4. Summary We developed laminated ultrathin membranes that could be handled even when the thickness was 10 μm or less, by combining a PFSA (Nafion and Aquivion) polymer with vinylon and laminating it with PFSA polymer. From the I–V evaluation of the fuel cells using the ultrathin PFSA/PFSA-vinylon/PFSA membranes, the cell resistances were low in comparison to those using the Nafion212 membrane, and high performances were obtained. Moreover, when oxygen was used as the cathode gas, the performance was remarkably high. We propose that laminating ultrathin PFSA-vinylon membranes with PFSA is a good method for lowering costs, achieving high performance and eliminating the need for a reinforcing material. Author Contributions: Conceptualization, J.-D.K.; methodology, J.-D.K.; validation, J.-D.K.; formal analysis, J.-D.K., K.Y., H.I., Y.T.; investigation, J.-D.K.; data curation, J.-D.K., K.Y., writing-Original draft preparation, J.-D.K.; writing-Review and editing, J.-D.K. All authors have read and agreed to the published version of the manuscript. Figure 4. I–V characteristics of (i) Nafion212, (ii) Nafion/Nafion-vinylon/Nafion, and (iii) Aquivion/Aquivion-vinylon/Aquivion at 80 ◦C in (a) air and (b) O2 under 100% RH and in (c) air and (d) O2 under 35% RH.Table 1. I–V performance summary for the (i) Nafion212, (ii) Nafion/Nafion-vinylon/Nafion, and (iii)Aquivion/Aquivion-vinylon/Aquivion membranes.Membranes100% RH 35% RHAir O2 Air O2Resistance(mohm) at0.3 A/cm2Rate (%) ofDecreasingResistanceResistance(mohm) at2.5 A/cm2Rate (%) ofDecreasingResistanceResistance(mohm) at0.3 A/cm2Rate (%) ofDecreasingResistanceResistance(mohm) at2.5 A/cm2(i) 15.6 100 20.8 100 60.8 100 _(ii) 6.5 45 8.0 38 16.7 27 26.4(iii) 6.5 45 7.7 37 25.1 41 20.34. SummaryWe developed laminated ultrathin membranes that could be handled even when the thickness was10 µm or less, by combining a PFSA (Nafion and Aquivion) polymer with vinylon and laminating it withPFSA polymer. From the I–V evaluation of the fuel cells using the ultrathin PFSA/PFSA-vinylon/PFSAmembranes, the cell resistances were low in comparison to those using the Nafion212 membrane,and high performances were obtained. Moreover, when oxygen was used as the cathode gas,the performance was remarkably high. We propose that laminating ultrathin PFSA-vinylon membraneswith PFSA is a good method for lowering costs, achieving high performance and eliminating the needfor a reinforcing material.Author Contributions: Conceptualization, J.K.; methodology, J.K.; validation, J.K.; formal analysis, J.K., K.Y.,H.I., Y.T.; investigation, J.K.; data curation, J.K., K.Y., writing-Original draft preparation, J.K.; writing-Reviewand editing, J.K. All authors have read and agreed to the published version of the manuscript.Funding: This research received no external funding.Polymers 2020, 12, 1730 6 of 6Conflicts of Interest: The authors declare no conflict of interest.References1. Kusoglu, A.; Weber, A.Z. New insights into perfluorinated sulfonic-acid ionomers. Chem. Rev. 2017, 117,987–1104. [CrossRef] [PubMed]2. Kolde, J.A.; Bahar, B.; Wilson, M.S.; Zawodzinski, T.A.; Gottesfeld, S. Advanced composite polymer electrolytefuel cell membranes. Electrochem. Soc. Proc. 1995, 95, 193–201. [CrossRef]3. 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This article is an open accessarticle distributed under the terms and conditions of the Creative Commons Attribution(CC BY) license (http://creativecommons.org/licenses/by/4.0/).http://dx.doi.org/10.1021/acs.chemrev.6b00159http://www.ncbi.nlm.nih.gov/pubmed/28112903http://dx.doi.org/10.1149/199523.0193PVhttp://dx.doi.org/10.3390/wevj8020431http://dx.doi.org/10.1016/j.jpowsour.2006.09.108http://dx.doi.org/10.3390/polym12061354http://www.ncbi.nlm.nih.gov/pubmed/32560108http://dx.doi.org/10.3390/membranes10020031http://www.ncbi.nlm.nih.gov/pubmed/32085526http://dx.doi.org/10.1149/2.F05171ifhttp://creativecommons.org/http://creativecommons.org/licenses/by/4.0/. Introduction  Experimental  Results and Discussion  Summary  References